144 research outputs found
Cold diffuse interstellar medium of Magellanic Clouds: I. HD molecule and cosmic-ray ionization rate
HD molecule is one the most abundant molecule in the Universe and due to its
sensibility to the conditions in the medium, it can be used to constrain
physical parameters in the medium where HD resides. Lately we have shown that
HD abundance can be enhanced in the low metallicity medium. Large and Small
Magellanic Clouds give us an opportunity to study low metallicity galaxies in
details towards different sightlines due to their proximity to our Galaxy. We
revisited FUSE space telescope archival spectra towards bright stars in
Magellanic Clouds to search for HD molecules, associated with the medium of
these galaxies. We reanalysed H absorption lines and constrained HD column
density at the positions of H components. We detected HD towards 24
sightlines (including 19 new detections). We try to measure cosmic ray
ionization rate for several systems using measured ,
and in most cases get loose constraints due to insufficient quality of the FUSE
spectra.Comment: accepted for publication in MNRA
Molecular hydrogen absorption systems in Sloan Digital Sky Survey
We present a systematic search for molecular hydrogen absorption systems at
high redshift in quasar spectra from the Sloan Digital Sky Survey (SDSS) II
Data Release 7 and SDSS-III Data Release 9. We have selected candidates using a
modified profile fitting technique taking into account that the Ly
forest can effectively mimic H absorption systems at the resolution of SDSS
data. To estimate the confidence level of the detections, we use two methods: a
Monte-Carlo sampling and an analysis of control samples. The analysis of
control samples allows us to define regions of the spectral quality parameter
space where H absorption systems can be confidently identified. We find
that H absorption systems with column densities
can be detected in only less than 3% of SDSS quasar spectra. We estimate the
upper limit on the detection rate of saturated H absorption systems () in Damped Ly- (DLA) systems to be about 7%. We
provide a sample of 23 confident H absorption system candidates that would
be interesting to follow up with high resolution spectrographs. There is a
1 color excess and non-significant extinction excess
in quasar spectra with an H candidate compared to standard DLA-bearing
quasar spectra. The equivalent widths (EWs) of C II, Si II and Al III (but not
Fe II) absorptions associated with H candidate DLAs are larger compared to
standard DLAs. This is probably related to a larger spread in velocity of the
absorption lines in the H bearing sample.Comment: 17 pages, 17 figures, accepted for publication in MNRA
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